1. Review for chapter 8 Problem-solving practice

2. Calculating masses 1) Calculate the molecular mass of pentane 2) Calculate the formula mass of calcium sulfate 3) Calculate the molar mass of sodium carbonate Answers: 1) C 5 H 12 = 72.1 u 2) CaSO 4 = 136.2 u 2) CaSO 4 = 136.2 u 3) Na 2 CO 3 = 106.0 g 3) Na 2 CO 3 = 106.0 g

3. Conversions 1) What is the mass of 7.20 moles of CO 2 ? 2) How many moles of water molecules are there in 212 grams of water? 3) How many formula units are there in 5.00 moles of NaCl? Answers: 1) 7.20 moles CO 2 = 317 g CO 2 2) 212 g H 2 O = 11.8 moles H 2 O 2) 212 g H 2 O = 11.8 moles H 2 O 3) 5.00 moles NaCl = 3.01 x 10 24 3) 5.00 moles NaCl = 3.01 x 10 24

4. Percent Composition 1) Calculate the percent composition of potassium chromate 2) Which has a higher % of oxygen: potassium chromate or carbon dioxide? Answers: 1) 40.3% K, 26.8% Cr, 33.0% O 1) 40.3% K, 26.8% Cr, 33.0% O 2) CO 2 has 72.7% O, higher than K 2 CrO 4 2) CO 2 has 72.7% O, higher than K 2 CrO 4

5. Empirical Formula 1) What is the empirical formula for a compound that is 43.7% phosphorus and 56.3% oxygen? Name the compound. 2) Name the compound whose composition is 36.5% Na, 25.4% S, and 38.1% O. Answers: 1) P 2 O 5, diphosphorus pentaoxide 1) P 2 O 5, diphosphorus pentaoxide 2) Na 2 SO 3, sodium sulfite 2) Na 2 SO 3, sodium sulfite

6. Molecular formula A compound’s empirical formula is CH 3, and its molar mass is 75.0 g. What is its molecular formula? A compound’s empirical formula is CH 3, and its molar mass is 75.0 g. What is its molecular formula? Answer: C 5 H 15

7. Hydrate Formula A hydrate is found to be 54.3% cobalt(II) chloride and 45.7% water. Calculate the empirical formula of the hydrate, and name it. A hydrate is found to be 54.3% cobalt(II) chloride and 45.7% water. Calculate the empirical formula of the hydrate, and name it. Answer: CoCl 2 * 6 H 2 O Answer: CoCl 2 * 6 H 2 O cobalt(II) chloride hexahydrate cobalt(II) chloride hexahydrate

8. Molarity 1) Find the molarity of a solution made with 90.0 grams of NaOH in 500. mL 2) How many grams of NaOH are needed to make 100. mL of 0.25 M NaOH? 3) How many mL of 2.00 M NaOH can be made with 60.0 g of NaOH? Answers: 1) 4.50 M NaOH 2) 1.00 g NaOH 2) 1.00 g NaOH 3) 750. mL of 2.00 M NaOH 3) 750. mL of 2.00 M NaOH